Mobile IP is a solution for seamless mobility on a network such as, for instance, the global Internet or a private network, that is scalable, robust and secure, and that allows roaming hosts or “mobile nodes” such as, for instance, radios, phones, laptops, PDAs, etc., to maintain ongoing communications while changing their point of attachment to the network. Specifically, each mobile node is always identified by its home address (regardless of its current point of attachment to the network), which provides information about its point of attachment to a home network. However, when the mobile node is connected to the network outside of its home network, i.e. when visiting a foreign network or a foreign domain, the mobile node is also associated with a care-of address that provides information about its current point of attachment.
Mobile IP provides for a registration process for registering the care-of address with a network entity called a home agent (“HA”) whose point of attachment, i.e., its IP address, is in the mobile node's home network. The home agent is a router on the mobile node's home network that tunnels datagrams (also known in the art as data packets) for delivery to the mobile node when it is away from home, and maintains current location information for the mobile node. Registration is what enables the home agent to send the datagrams destined for the mobile node through a tunnel to the care-of address. After arriving at the end of the tunnel, each datagram is then delivered to the mobile node. Registration is typically done via a network entity called a foreign agent (“FA”) whose point of attachment is in the visited network and whose IP address is the care-of address for the mobile node. The foreign agent is a router on the mobile node's visited network that provides routing services to the mobile node when registered with the foreign agent. The foreign agent detunnels and delivers datagrams to the mobile node that were tunneled by the mobile node's home agent. For datagrams sent by the mobile node, the foreign agent may serve as a default router for registered mobile nodes.
There are, however, some shortcomings associated with mobile IP, especially given the explosion in the past ten years in the number of mobile nodes attached to the network. One such shortcoming is with respect to the above-mentioned registration process. Namely, when the home agent is several hops away from the mobile node, the roundtrip latency involved in the mobile IP registration process can be significant. Thus, it would be desirable to have a solution that would reduce this latency.
A Mobile IP Working Group of the Internet Engineering Task Force (“IETF”) has published a memo describing a regional registration process, i.e., a registration process that is local to the visited network, which addresses the latency in the mobile IP registration process. The regional signaling is performed via a network entity called a gateway foreign agent (“GFA”), which introduces a layer of hierarchy in the visited network that is above that of the foreign agent. Similar to the foreign agent, the gateway foreign agent is also a router on the foreign network. Regional registrations reduce the number of signaling messages to the home agent, and also reduce the signaling delay when a mobile node moves or roams from one foreign agent to another, i.e., changes foreign agents, within the same visited network.
However, a shortcoming of the regional registration approach, as described in the IETF memo, is that it requires changes to the mobile nodes. The mobile node must be aware of the presence of the gateway foreign agent and is, thereby, responsible for sending out regional registration requests to the gateway foreign agent, as well as regular registration requests to its home agent. It is, however, unrealistic to expect all mobile nodes to have support for this regional registration feature. Accordingly, many standard mobile IP, e.g., MIPv4, nodes will not benefit by the presence of the gateway foreign agent.
Thus, there exists a need for a regional registration solution that is compatible with mobile nodes that use a standard mobile IP protocol such as, for instance, MIPv4, and that, accordingly, does not require the mobile node to know about the GFA or the process of regional registration.